The present invention pertains to submersible pressure vessels and more particularly to lights utilized within the interior of the pressure vessel.
Lights used in submersible pressure vessels are commonly known. The lights for pressure vessels have various requirements. The light must produce the least possible dead angle and at the same time must be sufficiently bright for illuminating the whole pressure vessel. For safety purposes, the lamps used for the lights in submersible pressure vessels must have a surface temperature which does not exceed 60.degree. C.
The known lights for pressure vessels normally include filament lamps, which are covered with containers filled with a heat-conducting fluid. The fluid contained in such containers, usually water, is arranged in connection with an element having good heat conductivity. This element is usually a wall of the pressure vessel. In this case, heat produced by the filament lamp must be conducted to this wall.
It has been recognized that in such installations, only filament lamps having a power of 20 watts may be used in order to keep the maximum surface temperature within a limit of 60.degree. C. However, the illuminating of the pressure vessel with such lamps is not possible since the available candle power is not sufficient.
Lamps must be installed in the interior of the pressure vessel; however electrical cables must extend out from the pressure vessel. Since submersible pressure vessels often operate at a great depth and employ a helium-air environment, the cables must be reliably sealed against helium. Due to the small size of helium molecules even under normal pressure helium can enter inside the cables. During the decomposition of the pressure vessel the infiltrated helium then can not quickly enough escape from the cables so that a high over pressure may build up within the cables. This can lead to the formation of bubbles in the cables and eventually to damage to the cables.
A further disadvantage of known light installations is that the use of voltage in excess of 50 V is not allowed by regulations. Low voltage lamps must therefore be utilized for illuminating submersible pressure vessels. Such lamps, however, have a lower life-span than the commonly used 220 V lamps. Another disadvantage of the known installations resides in that because of insufficient power of these lamps a number of lamps must be installed in the pressure vessel. This leads to substantial restriction of the volume of the pressure vessel, which volume must be sufficient for movement of a person occupying the pressure vessel.
In order to avoid difficulties encountered in the prior art devices, it has been suggested to use a porthole in the pressure vessel. Light then enters the pressure vessel from lamps mounted outside the pressure vessel. In such installation, the illuminating of the pressure vessel is not sufficiently good. Even if a number of such portholes are provided there are still areas in the pressure vessel which can be not sufficiently illuminated since the number of port-holes has to stay within reason. (It must not be so large as to weaken the structural strength of the vessel wall).